A conventional imaging device is disclosed, for example, in JP 2001-78213A. FIG. 50 is a cross-sectional view showing the configuration of the conventional imaging device.
In FIG. 50, an imaging system 9010 is an optical processing system that images light from an object on the imaging surface of an imaging element 9120 via an aperture 9110 and an imaging lens 9100. The aperture 9110 has three circular openings 9110a, 9110b and 9110c. The object light from the openings 9110a, 9110b and 9110c that is incident on a light incidence surface 9100e of the imaging lens 9100 is emitted from three lens units 9100a, 9100b and 9100c of the imaging lens 9110 and forms three object images on the imaging surface of the imaging element 9120. A shading film is formed on a flat portion 9100d of the imaging lens 9100. Three optical filters 9052a, 9052b and 9052c that transmit light of different wavelength ranges are formed on the light incidence surface 9100e of the imaging lens 9100. Three optical filters 9053a, 9053b and 9053c that transmit light of different wavelength ranges are also formed on three imaging areas 9120a, 9120b and 9120c on the imaging element 9120. The optical filters 9052a and 9053a have a spectral transmittance characteristic of mainly transmitting green (marked G), the optical filters 9052b and 9053b have a spectral transmittance characteristic of mainly transmitting red (marked R), and the optical filters 9052c and 9053c have a spectral transmittance characteristic of mainly transmitting blue (marked B). Thus, the imaging areas 9120a, 9120b and 9120c are respectively sensitive to green (G), red (R) and blue (B) light.
With an imaging device such as this having a plurality of imaging lenses, the mutual spacing between the plurality of object images respectively formed by the plurality of imaging lenses on the imaging surface of the imaging element 9120 changes when the distance from the camera module to the object changes.
With the above conventional camera module, the optical axis spacing of the plurality of imaging systems is set such that the mutual spacing between the plurality of object images when the object is at a virtual subject distance D[m] and the mutual spacing between the plurality of object images when the object is at infinity changes by less than twice the pixel pitch of a reference image signal, where D=1.4/(tan θ/2), with the virtual subject distance D[m] as a function of the angle of view θ[°] of the plurality of imaging systems. That is, color shift in the images of an object at infinity can be suppressed to a permissible level, even when the same image processing optimized for capturing an image of an object at a virtual subject distance D[m] is performed on an object at infinity, because the optical axis spacing is set such that the difference in mutual spacing between the two sets of object images on the imaging surface will be less than twice the pixel pitch of a reference signal.
In the conventional imaging device, the optical axes of the three lens units 9100a, 9100b and 9100c of the imaging lens 9100 are disposed so as to pass respectively through the centers of the three circular openings 9110a, 9110b and 9110c of the aperture 9110 and the centers of the imaging areas 9120a, 9120b and 9120c. However, the optical axes of the three lens units 9100a, 9100b and 9100c of the imaging lens 9100 can deviate from the respective centers of the three circular openings 9110a, 9110b and 9110c of the aperture 9110 due to variability in component precision, assembly or the like. A characteristic particular to the lens is that the light intensity around the periphery of the imaging surface of the imaging element 9120 (peripheral brightness) decreases in comparison to the center, although the extent to which peripheral brightness decreases differs when the optical axes of the three lens units 9100a, 9100b and 9100c of the imaging lens 9100 deviate in different directions from the centers of the three circular openings 9110a, 9110b and 9110c of the aperture 9110.
FIG. 51 illustrates the relationship between the aperture, the lens units, and peripheral brightness. In FIG. 51, only the lens 9100, the aperture 9110 and the imaging element 9120 are shown for simplicity. The curves marked G, R and B show the respective light intensities of the colors green, red and blue. Here, the positive sense of the y direction is upwards on the page, as shown in FIG. 51. As in FIG. 51, the peripheral brightness on the imaging surface of the imaging element 9120 decreases symmetrically in the positive and negative senses of the y direction, when the center of the circular opening 9110b coincides with the optical axis of the lens unit 9110b (curved distribution marked R). Thus, the light intensity distribution for red is positively and negatively symmetrical in relation to the y direction. However, when the center of the circular opening 9110a deviates from the optical axis of the lens unit 9100a in the negative sense of the y direction, the peripheral brightness on the imaging surface of the imaging element 9120 decreases to a greater extent in the negative sense of the y direction (curved distribution marked G). Thus, the light intensity distribution for green is pronounced in the positive sense in relation to the y direction. On the other hand, when the center of the circular opening 9110c deviates from the optical axis of the lens unit 9100c in the positive sense of the y direction, due to variability in processing precision of the lends 9100 or the apertures 9110, brightness on the imaging surface of the imaging element 9120 decreases to a greater extent in the positive sense of the y direction (curved distribution marked B). Thus, the light intensity distribution for blue is pronounced in the negative sense in relation to the y direction. Note that when the aperture 9110 and the lens 9100 are made from thermoformed resin, variability as in FIG. 51 can arise from differences in the coefficient of thermal expansion resulting from compositional differences.
FIG. 52 shows the light intensity distributions for the green, red and blue components. The y-axis is shown on the horizontal axis and light intensity is shown on the vertical axis. Where, for example, images of a gray subject are captured and synthesized when the above variability is present, colors (false color) other than the actual colors (gray in the present example) of the subject are produced, such as red in central portions in the y direction, green in positive positions, and blue in negative positions, since the light intensity distribution for red (curve marked R) will be positively and negatively symmetrical in relation to the y direction, the light intensity distribution for green (curve marked G) will be pronounced in the positive sense in relation to the y direction, and the light intensity distribution for blue (curve marked B) will be pronounced in the negative sense in relation to the y direction, as shown in FIG. 52. That is, a conventional imaging device that has a plurality of lens units and receives red, green and blue light of the subject independently in imaging areas corresponding respectively to the lens units produces false colors when the light intensity distribution is biased because of differing light intensities for red, green and blue light.
False colors thus are produced when the light axes of the three lens units 9100a, 9100b and 9100c of the imaging lens 9100 deviate from the respective centers of the circular openings 9110a, 9110b and 9110c of the aperture 9110 due to variability in component precision, assembly or the like.
Note that the above problem does not arise with an imaging device constituted by a single lens unit and a single imaging area, and having an imaging element in which a Bayer array of color filters is disposed in the imaging area (e.g., imaging element is a CCD, and has 3 different color filters red, green and blue disposed in a lattice on the surface of the imaging element, each color filter corresponding to a different photodiode). That is, false colors are not produced even if the lens unit deviates from the center of the aperture and light intensities are biased due to the aforementioned variability in component precision, assembly or the like, because the light intensity distributions for red, green and blue will be similar, since the red, green and blue color filters are disposed in a lattice in proximity to each other, and the red, green and blue light of the subject is received at an imaging area that brings them close together. However, the size and profile of an imaging device constituted by a single lens unit and a single imaging element cannot be reduced because of the long optical length.